In patients suffering a lack of a renal function or a liver function, harmful toxic substances are accumulated or formed in bodies, such as blood, with a progress of a disorder of the organ functions, and thus an encephalopathia occurs, such as a disturbance of consciousness or uremia. Yearly, there is a growing number of such patients, and therefore, the development of an organ-substitute apparatus or medicament having a function to remove toxic substances from bodies, in place of such defective organs, has become a serious problem. A method for removing toxic substances by hemodialysis as an artificial kidney is prevalent. Nevertheless, the hemodialysis-based artificial kidney requires a special apparatus, and thus, a skilled specialist is required from a safe operation standpoint. Further, blood must be taken from a patient's body, and thus, there are disadvantages in that patients must bear high physical, mental and economic burdens. Accordingly, hemodialysis is not satisfactory.
As a means of remedying the above disadvantages, an oral adsorbent which can be orally administered and cure a disorder of renal and liver functions was developed and utilized [Patent Reference No. 1]. The adsorbent disclosed in Patent Reference No. 1 comprises a porous surface-modified spherical carbonaceous substance having particular functional groups, that is, a surface-modified spherical activated carbon, having a high safety factor and stable to a body, and having a useful selective adsorbability; that is, an excellent adsorbability of harmful substances in the presence of a bile acid in an intestine, and a low adsorbability of useful substances such as digestive enzymes in the intestine. For these reasons, the oral adsorbent is widely and clinically used for a patient suffering from a disorder of a liver or renal function, as an adsorbent having few side effects such as constipation. The above adsorbent disclosed in Patent Reference No. 1 was prepared by forming a spherical activated carbon from a pitch such as a petroleum pitch as a carbon source, and then carrying out an oxidizing treatment and a reducing treatment.
Further, an adsorbent for an oral administration providing an improvement in the above useful selective adsorbability, that is, an excellent adsorbability of harmful substances and a low adsorbability of useful substances in the intestine, is known (Patent Reference No. 2). The adsorbent for an oral administration disclosed in Patent Reference No. 2 is based on a finding that the above selective adsorbability is improved within a special range of a pore volume, that is, when a volume of pores having a pore diameter of 20 to 15000 nm is from not less than 0.04 mL/g to less than 0.10 mL/g. The adsorbent for an oral administration is very effective in treating diseases where a sufficient adsorption of toxins and a reduced adsorption of useful substances in the intestine are desired.
Further, a medical adsorbent composed of an activated carbon having a specific surface area of 500 to 2000 m2/g, a pore volume of 0.2 to 1.0 mL/g, and a bulk density of 0.5 to 0.75 g/mL, and prepared by carbonizing and activating spherical phenol resin is known (Patent Reference No. 3). Patent Reference No. 3 mentions that the medical adsorbent disclosed therein is composed of the activated carbon having controlled properties of the specific surface area, the pore volume, the average pore diameter, the particle size, and the amount of oxides on the surface, and thus, can selectively adsorb ionic organic compounds while inhibiting the adsorption of polymers, such as polysaccharides or enzymes, necessary for a body.
It is known that, in a patient suffering from chronic renal failure, a concentration of indoxyl sulfuric acid in serum may be increased about 60 times higher than that in a healthy person, and that a concentration of indoxyl sulfuric acid in serum can be lowered, and thus, the progress of the chronic renal failure can be delayed by an administration of the oral adsorbent disclosed in the above Patent Reference No. 1 (Non-patent Reference Nos. 1 and 2). The mechanism whereby a concentration of indoxyl sulfuric acid is increased in a patient suffering from chronic renal failure is assumed as follows. That is, a part of tryptophan derived from proteins is metabolized to indole by Escherichia coli or the like in an intestinal tract. The indole is taken up, and converted by a sulfate conjugation to indoxyl sulfuric acid in a liver. The produced indoxyl sulfuric acid is excreted from a kidney of a healthy person. However, the excretory pathway is inhibited in a patient suffering from chronic renal failure, and thus, indoxyl sulfuric acid is accumulated in blood.    [Patent Reference No. 1]
Japanese Examined Patent Publication (Kokoku) No. 62-11611    [Patent Reference No. 2]
Japanese Patent No. 3522708 (Japanese Unexamined Patent Publication (Kokai) No. 2002-308785)    [Patent Reference No. 3]
Japanese Unexamined Patent Publication (Kokai) No. 2004-24414    [Non-patent Reference No. 1]
Nichijinkaishi (The Japanese journal of nephrology), vol. 32, No. 6, 1990, pp 65-71    [Non-patent Reference No. 2]
Rinsho-Toseki (The Japanese Journal of Clinical Dialysis), vol. 14, No. 4, 1998, pp 433-438